Measuring tips to assure the best fit of your top

Shoulders. Back (Standard) width.
Think of a line going from your armpit straight upwards to your shoulder. Measure between those two points and hold the tape measure straight. If you are wearing a dress shirt that fits your upper body correctly, you can use it as a guide. The shoulder seams on the back of your shirt will usually match up with your actual shoulder points.
Chest.
The chest measurement is taken as a circumference measurement around your chest at the widest point. Stand in a relaxed posture and breathe out.
Sleeve length.
Measure the length from the top stitching on the shoulder to the bottom of the wrist. Aim for hitting your wrist bone with the measuring tape. Be careful not to measure too high above the wrist, or the dress shirt’s sleeves will come to be too short.